Switching regulator compatible with electronic transformer and control method thereof

ABSTRACT

The present invention discloses a switching regulator compatible with an electronic transformer and a control method thereof. The switching regulator includes: a power stage circuit, a control circuit, and an input current peak &amp; valley setting circuit. The control circuit is coupled to the power stage circuit, for generating an operation signal according to a feedback signal and a peak &amp; valley setting signal, to operate at least one power switch in the power stage circuit, so as to convert a rectified input voltage to an output voltage. The input current peak &amp; valley setting circuit is coupled to the control circuit, for generating the peak &amp; valley setting signal such that in one cycle period, the input current has multiple valleys forming a semi-sinusoidal contour.

CROSS REFERENCE

The present invention claims priority to U.S. Ser. No. 61/817112, filedon Apr. 29, 2013.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a switching regulator compatible withan electronic transformer and a control method thereof; particularly, itrelates to such switching regulator and control method thereof whereinan input current is related to a difference between an output voltageand a rectified input voltage.

2. Description of Related Art

FIG. 1A shows a schematic diagram of a prior art switching regulator 100and an electronic rectifier circuit 110. As shown in FIG. 1A, theswitching regulator 100 includes a power stage circuit 10, a controlcircuit 20, and a feedback circuit 30. The power stage circuit 10receives a rectified input voltage Vin, and converts the rectified inputvoltage Vin to an output voltage Vout according to an operation signalGATE. The rectified input voltage Vin is generated by the electronicrectifier circuit 110. The electronic rectifier circuit 110 includes anelectronic transformer 40 and a rectifier circuit 50. The electronictransformer 40 receives an AC voltage VAC and converts it to an ACvoltage VAC′ which has a lower amplitude. The rectifier circuit 50receives the AC voltage VAC′, and rectifies it to generate the rectifiedvoltage Vin. The feedback circuit 30 generates a feedback signal FBaccording to the output voltage Vout. The control circuit 20 isconnected to the feedback circuit 30 to receive the feedback signal FB,and it generates the operation signal GATE according to the feedbacksignal FB to operate a power switch (not shown, referring to FIGS.2A-2K) in the power stage circuit 10, so as to convert the rectifiedinput voltage Vin to the output voltage Vout, and to control an inputcurrent Iin. The power stage circuit 10 may be a synchronous orasynchronous buck, boost, inverting, buck-boost, inverting-boost, orflyback power stage circuit as shown in FIGS. 2A-2K.

The reason that the electronic rectifier circuit 110 uses the electronictransformer 40 is for decreasing the size of the entire circuitry, suchthat the switching regulator 100 may be applied in an electronic productsuch as a wall lamp or a downlight. The electronic transformer 40converts the AC voltage VAC having a higher amplitude, such as 110V or220V, to the AC voltage VAC′ having a lower amplitude, such as 12V or14V. The electronic transformer 40 is well known by those skilled in theart, so details thereof are omitted here.

FIG. 1B is a schematic diagram showing signal waveforms of the ACvoltages VAC and VAC′, the rectified voltage Vin, and the output voltageVout. In FIG. 1B, the thin solid lines indicate a zero level or a groundlevel, and the thick solid lines indicate the signal waveforms of theaforementioned signals. As shown in the figure, the AC voltage VAC has arelatively higher amplitude (the amplitudes in the figure are not shownin actual scale). The electronic transformer 40 oscillates with afrequency higher than the AC voltage VAC, and generates the AC voltageVAC′ as shown in FIG. 1B. For example, the frequency of the AC voltageVAC is 60 Hz, and the electronic transformer 40 oscillates with afrequency for example of 30 kHz in one cycle period, to generate the ACvoltage VAC′ having a contour as shown which has a frequency of 120 Hz.The AC voltage VAC′ is rectified to the semi-sinusoidal rectifiedvoltage Vin having a frequency of 120 Hz. The output voltage Vout forexample has a fixed level.

In the aforementioned prior art switching regulator 100, the powerconversion is achieved by switching one or more power switches in powerstage circuit 10, and the switching of the power switch determines theinput current Iin. To achieve power factor correction (PFC) for betterpower factor, in this prior art, a typical method is to control theswitching of the power switch such that the peaks (Iin_max) of the inputcurrent form a contour which is substantially in phase with therectified input voltage Vin, as indicated by FIG. 1C. However, as abasic requirement of the electronic transformer 40, the peaks of itsload current (the input current Iin is the load current of theelectronic transformer 40) must be higher than a minimum load currentIload_min, otherwise the electronic transformer 40 does not operate. Inthis prior art, because it is uncertain as to what kind of electronictransformer 40 and what kind of switching regulator 100 a user mightuse, and different electronic transformers 40 have differentspecifications, the peaks (Iin_max) of the input current Iin might belower than the minimum load current Iload_min, and in some extremecases, the electronic transformer 40 may not be able to operate in anentire cycle period of the rectified input voltage Vin, resulting inpoor compatibility of the switching regulator 100 and the electronicrectifier circuit 110.

In view of above, the present invention proposes a switching regulatorcompatible with an electronic transformer and a control method thereof.

SUMMARY OF THE INVENTION

From one perspective, the present invention provides a switchingregulator compatible with an electronic transformer, for converting arectified input voltage to an output voltage, wherein the rectifiedinput voltage is generated by an electronic rectifier circuit whichincludes the electronic transformer and a rectifier circuit coupled toeach other, the switching regulator comprising: a power stage circuit,for switching at least one power switch therein according to anoperation signal to convert the rectified input voltage to the outputvoltage, and to control an input current flowing from the electronicrectifier circuit to the switching regulator; a control circuit, whichis coupled to the power stage circuit, for generating the operationsignal according to a feedback signal and an input current peak andvalley setting (P&Vset) signal; and an input current peak and valleysetting circuit, which is coupled to the control circuit, for generatingthe P&Vset signal, wherein the input current has a plurality of peaksand valleys in one cycle period, wherein the plural valleys form asemi-sinusoidal contour, and the plural peaks have a predetermined fixedlevel higher than the plural valleys or predetermined variable levelshigher than the plural valleys.

From another perspective, the present invention provides a controlmethod of a switching regulator compatible with an electronictransformer, for converting a rectified input voltage to an outputvoltage, wherein the rectified input voltage is generated by anelectronic rectifier circuit which includes the electronic transformerand a rectifier circuit coupled to each other, the control methodcomprising: switching at least one power switch in the switchingregulator according to an operation signal to convert the rectifiedinput voltage to the output voltage and control an input current flowingfrom the electronic rectifier circuit to the switching regulator;generating the operation signal according to a feedback signal and aninput current peak and valley setting (P&Vset) signal; and generatingthe P&Vset signal according to a difference of the output voltage andthe rectified input voltage, wherein the input current has a pluralityof peaks and valleys in one cycle period, wherein the plural valleysform a semi-sinusoidal contour, and the plural peaks have apredetermined fixed level higher than the plural valleys orpredetermined variable levels higher than the plural valleys.

In one preferable embodiment, the power stage circuit turns OFF thepower switch for a predetermined fixed time period according to theoperation signal.

In one preferable embodiment, the plural peaks in the one cycle periodform a semi-sinusoidal contour.

In one preferable embodiment, the input current is related to adifference between the output voltage and the rectified input voltage.

In one preferable embodiment, the input current includes a DC componentand a semi-sinusoid component.

The objectives, technical details, features, and effects of the presentinvention will be better understood with regard to the detaileddescription of the embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a schematic diagram of a prior art switching regulator 100and an electronic rectifier circuit 110.

FIG. 1B is a schematic diagram showing signal waveforms of the ACvoltages VAC and VAC′, the rectified voltage Vin, and the output voltageVout.

FIG. 1C is a schematic diagram showing signal waveforms of the inputcurrent Iin, the peaks (Iin_max) of the input current Iin, and theminimum load current Iload_min in the prior art.

FIGS. 2A-2K show synchronous and asynchronous buck, boost, inverting,buck-boost, inverting-boost, and flyback power stage circuits.

FIG. 3 shows a hardware embodiment of the present invention.

FIG. 4A is a schematic diagram showing signal waveforms of the rectifiedinput voltage Vin, the output voltage Vout, and the voltage differenceof Vout−Vin in the present invention.

FIG. 4B is a schematic diagram showing signal waveforms of the inputcurrent Iin, the peaks Iin_max of the input current Iin, the averageIin_ave of the input current Iin, and the minimum load current Iload_minin an embodiment of the present invention.

FIG. 4C shows an analysis of the components of the average input currentIin_ave in an embodiment of the present invention.

FIG. 4D is a schematic diagram showing signal waveforms of the inputcurrent Iin and the peaks Iin_max of the input current Iin in anotherembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer to FIG. 3 for an embodiment according to the presentinvention. As shown in FIG. 3, a switching regulator 200 includes apower stage circuit 10, a control circuit 20, a feedback circuit 30, andan input current peak & valley setting circuit 60. The power stagecircuit 10 converts the rectified input voltage Vin to the outputvoltage Vout according to the operation signal GATE, and controls theinput current Iin according to the operation of the power switch (notshown in FIG. 3, referring to FIGS. 2A-2K). The electronic rectifiercircuit 110 includes the electronic transformer 40 and the rectifiercircuit 50. The electronic transformer 40 receives the AC voltage VAC,and converts it to the AC voltage VAC′ which has a lower amplitude. Therectifier circuit 50 receives the AC voltage VAC′, and rectifies it togenerate the rectified voltage Vin. The schematic signal waveforms ofthe AC voltages VAC and VAC′, the rectified input voltage Vin, and theoutput voltage Vout are shown in FIG. 1B. The feedback circuit 30generates the feedback signal FB according to the output voltage Vout.The control circuit 20 is coupled to the feedback circuit 30, and itgenerates the operation signal GATE according to the feedback signal FB,to operate at least one power switch (not shown in FIG. 3, referring toFIGS. 2A-2K), so as to convert the rectified input voltage Vin to theoutput voltage Vout, and control the input current Iin. If the powerstage circuit 10 includes two or more power switches, the operationsignal GATE may correspondingly include plural operation signals, aswell known by those skilled in the art; therefore, the details thereofare omitted here. The power stage circuit 10 is for example but notlimited to the synchronous or asynchronous buck, boost, inverting,buck-boost, inverting-boost, or flyback power stage circuit as shown inFIGS. 2A-2K. This embodiment is different from the prior art switchingregulator 100 in that, the switching regulator 200 further includes aninput current peak & valley setting circuit 60, which is coupled to thecontrol circuit 20, for generating an input current peak and valleysetting (P&Vset) signal, to control the input current Iin such that theinput current Iin has plural peaks and valleys in one cycle period,wherein the plural valleys form a semi-sinusoidal contour, and theplural peaks have a predetermined fixed level or predetermined variablelevels higher than the plural valleys.

In one embodiment, as described in the above, the frequency of the ACvoltage VAC is for example 60 Hz; the frequency of the AC voltage VAC′is 120 Hz; and the electronic transformer 40 oscillates by a frequencyfor example of 30 kHz. Preferably, the power switch of the power stagecircuit 10 switches by a frequency of, for example but not limited to,300 kHz or above. In a preferable embodiment, the power switch of thepower stage circuit 10 switches by a frequency at least times higherthan the oscillation frequency of the electronic transformer 40.

Referring to FIG. 4B, the present invention is different from the priorart switching regulator at least in the following aspect. The controlcircuit 20 generates the operation signal GATE according to a differenceof the output voltage Vout and the rectified input voltage Vin, tocontrol the input current Iin such that in one cycle period, the inputcurrent Iin has plural valleys, and the plural valleys form asemi-sinusoidal contour. Thus, the switching regulator according to thepresent invention provides the effect of power factor correction (PFC),while in the mean time the peaks Iin_max of the input current Iin arehigher than the minimum load current Iload_min. According to basicoperation of the switching regulator 200, when the power switch of thepower stage circuit 10 is ON, an inductor in the power stage 10 circuit(referring to FIGS. 2A-2K) storages energy, so that the input currentIin increases; when the power switch in the power stage circuit 10 isOFF, the inductor in the power stage circuit 10 releases energy, so thatthe input current Iin decreases. Therefore, in one embodiment which isfor example but not limiting, the turned-ON and turned-OFF timings ofthe power switch may be controlled to generate a desired signal waveformof the input current Iin. More specifically, an upper limit of the inputcurrent Iin may be set according to a predetermined peak level (in theembodiment of FIG. 4B, the upper limit is constant, but it can be apredetermined variable in another embodiment), and a lower limit of theinput current Iin may be set according to the semi-sinusoidal contour(in the embodiment of FIG. 4B, the lower limit is the semi-sinusoid).Thus, the power switch can be turned ON until the input current Iinincreases to the peak, and then the power switch is turned OFF so thatthe inductor of the power stage circuit 10 stops storing energy; and asthe input current Iin decreases to the lower limit, the power switch isturned ON so that the inductor of the power stage circuit 10 stopsreleasing energy. As the diagram shows, even if the specification of theelectronic transformer 40 is unknown, the peaks of the input currentIin_max can be easily ensured higher than the minimum load currentIload_min of the electronic transformer 40.

FIG. 4D shows a second embodiment of the present invention. Thisembodiment is different from the first embodiment in that, the peaksIin_max of the input current Iin are set to a semi-sinusoid contour(referring to FIG. 4D) instead of a fixed level by the input currentpeak & valley setting circuit 60, such that the PFC effect may befurther improved. To generate the semi-sinusoidal contour of the peaksIin_max of the input current Iin, it is required to obtain informationrelated to the cycle period or the phase of the rectified input voltageVin, and such information may be obtained from, for example but notlimited to, the input voltage Vin, the AC voltage VAC, the AC voltageVAC′, a divided voltage of any of the above, or any signal which hassuch cycle period information or phase information.

More specifically, as an example, let us assume that the power stagecircuit 10 includes the boost power stage circuit as shown in FIG. 2Dand the peaks Iin_max of the input current Iin have a fixed level asshown in the first embodiment. The input current Iin flows through theinductor of the boost power stage circuit. The current flowing throughthe inductor (the inductor current) is: di=(Vout−Vin)×dt/L, wherein diis the inductor current, L is the inductance of the inductor of theboost power stage circuit, and dt is time. Since the inductance L is aconstant, and the time dt can be fixed because in the power stagecircuit 10, the OFF period of the power switch can be set to apredetermined fixed time, the inductor current di becomes a function ofthe voltage difference (Vout−Vin) , i.e., di=f (Vout−vin) . Thus, theinput current Iin can be controlled to include plural valleys in onecycle period, and the plural valleys form a semi-sinusoidal contouraccording to the aforementioned equation as indicated by the dashedsemi-sinusoid shown in FIG. 4B.

Certainly, the aforementioned method for forming the semi-sinusoidalcontour is only one non-limiting embodiment according to the presentinvention. For example, in another embodiment, the semi-sinusoidalcontour may be formed by detecting the input current or its relatedsignal (such as the inductor current), and comparing the detected signalwith reference signals which include the settings of the peaks and thevalleys.

Still referring to FIG. 4B, in one cycle period, the input current Iinhas plural peaks which have a constant level (Iin_max), and has pluralvalleys which form the semi-sinusoidal contour. Therefore, the averageinput current Iin_ave is an average of the peak and the valley whichbasically has a same phase as the rectified input voltage Vin, asindicated by the thick dashed semi-sinusoid shown in FIG. 4B. Thus, thepresent invention can improve the power factor. From anotherperspective, referring to FIG. 4C, the input current Iin shown in FIG.4B may be divided to two components, wherein one component is a DCcomponent Iin_dc and the other component is a semi-sinusoid componentIin_sin, and the average input current Iin_ave is a sum of the DCcomponent and the AC component.

A comparison of FIGS. 1C and 4B shows the advantage of the presentinvention over the prior art. In the present invention, thesemi-sinusoidal contour is formed by the valleys of the input currentIin, and the peaks of the input current Iin are Iin_max which iscertainly higher than the valleys, so the peaks of the input currentIin_max can be easily ensured higher than the minimum load currentIload_min of the electronic transformer 40. In the prior art, thesemi-sinusoidal contour is formed by the peaks of the input current Iin,and the peaks of the input current Iin_max may very likely be lower thanthe minimum load current Iload_min of the electronic transformer 40 atleast in a portion of one cycle period, and therefore, the switchingregulator 100 and the electronic rectifier circuit 110 may not be ableto cooperate with each other. In comparison with the prior art, thepresent invention can improve the compatibility of the switchingregulator 200 and the electronic transformer 40.

FIG. 4D shows that the peaks of the input current Iin_max are notlimited to the fixed level as shown in FIG. 4B, but may form asemi-sinusoid instead, such that the PFC effect may be further improved.In this case, the peaks of the input current Iin_max might be lower thanthe minimum load current Iload_min at the beginning and/or the end ofone cycle period. According to the present invention, this problem maybe solved by keeping the power switch ON at the beginning and/or the endof the cycle period.

The present invention has been described in considerable detail withreference to certain preferred embodiments thereof. It should beunderstood that the description is for illustrative purpose, not forlimiting the scope of the present invention. Those skilled in this artcan readily conceive variations and modifications within the spirit ofthe present invention. For example, a device or circuit which does notsubstantially influence the primary function of a signal can be insertedbetween any two devices or circuits shown to be in direct connection inthe embodiments, such as a switch or the like, so the term “couple”should include direct and indirect connections. For another example, thepower stage circuit that is applicable to the present invention is notlimited to the boost power stage circuit as shown and described in theembodiments above, but may be any synchronous or asynchronous buck,boost, inverting, buck-boost, inverting-boost, or flyback power stagecircuit as shown in FIGS. 2A-2K, with corresponding amendments of thecircuits or the signals. In view of the foregoing, the spirit of thepresent invention should cover all such and other modifications andvariations, which should be interpreted to fall within the scope of thefollowing claims and their equivalents.

What is claimed is:
 1. A switching regulator compatible with an electronic transformer, for converting a rectified input voltage to an output voltage, wherein the rectified input voltage is generated by an electronic rectifier circuit which includes the electronic transformer and a rectifier circuit coupled to each other, the switching regulator comprising: a power stage circuit, for switching at least one power switch therein according to an operation signal to convert the rectified input voltage to the output voltage, and to control an input current flowing from the electronic rectifier circuit to the switching regulator; a control circuit, which is coupled to the power stage circuit, for generating the operation signal according to a feedback signal and an input current peak and valley setting (P&Vset) signal; and an input current peak and valley setting circuit, which is coupled to the control circuit, for generating the P&Vset signal, wherein the input current has a plurality of peaks and valleys in one cycle period, wherein the plural valleys form a semi-sinusoidal contour, and the plural peaks have a predetermined fixed level higher than the plural valleys or predetermined variable levels higher than the plural valleys.
 2. The switching regulator of claim 1, wherein the power stage circuit turns OFF the power switch for a predetermined fixed time period according to the operation signal.
 3. The switching regulator of claim 1, wherein the plural peaks in the one cycle period form a semi-sinusoidal contour.
 4. The switching regulator of claim 1, wherein the input current is related to a difference between the output voltage and the rectified input voltage.
 5. The switching regulator of claim 1, wherein the input current includes a DC component and a semi-sinusoid component.
 6. A control method of a switching regulator compatible with an electronic transformer, for converting a rectified input voltage to an output voltage, wherein the rectified input voltage is generated by an electronic rectifier circuit which includes the electronic transformer and a rectifier circuit coupled to each other, the control method comprising: switching at least one power switch in the switching regulator according to an operation signal to convert the rectified input voltage to the output voltage and control an input current flowing from the electronic rectifier circuit to the switching regulator; generating the operation signal according to a feedback signal and an input current peak and valley setting (P&Vset) signal; and generating the P&Vset signal according to a difference of the output voltage and the rectified input voltage, wherein the input current has a plurality of peaks and valleys in one cycle period, wherein the plural valleys form a semi-sinusoidal contour, and the plural peaks have a predetermined fixed level higher than the plural valleys or predetermined variable levels higher than the plural valleys.
 7. The control method of claim 6, wherein the operation signal turns OFF the power switch for a predetermined fixed time period.
 8. The control method of claim 6, wherein the plural peaks in the one cycle period form a semi-sinusoidal contour.
 9. The control method of claim 6, wherein the input current is related to a difference of the output voltage and the rectified input voltage.
 10. The control method of claim 6, wherein the input current includes a DC and a semi-sinusoid current. 